A master circuit designates a circuit that may control at least one other circuit, called a slave circuit. The slave circuit performs according to instructions dictated by the master circuit. For example, a state machine may be used to produce control sequences for logic circuits that have specific functions, e.g., counters, memories, and arithmetic logic units. These control sequences may or may not be conditional.
Conventionally, the state machine enables the performance of a sequence of operations for producing control signals for controlling a slave circuit. The frequency of operations of the state machine is generally controlled by a clock signal f.sub.1. In general, the state machine sends logic commands to the slave circuits by a control bus to which a sequencer and the slave circuits are connected. The logic commands include writing or reading information on a data bus. It is also possible that the sequencer may send a command to a particular slave circuit operating at a frequency f.sub.2 for carrying out at least one operation in parallel.
In general, the state machine does not verify whether a particular slave circuit has received the command to be performed. Accordingly, the state machine limits itself, for example, to sending a command during a time interval in which the state machine is sure that the slave circuit will receive this command.
When the state machine and the slave circuit are synchronous, the state machine may send a command having a determined duration corresponding to a certain number of clock cycles. The synchronization between the state machine and the slave circuit makes it possible to ensure efficient reception. Synchronous refers to when the clock frequencies f.sub.1 and f.sub.2 are identical to or multiples of one another with respect to the clock signals originating from the same clock.
In contrast, when the clock frequency f.sub.1 of the state machine and the clock frequency f.sub.2 of the slave circuit are not synchronous, the reception of the control signal by the slave sequencer may become random. This could lead to malfunctioning of the integrated circuit. Not synchronous, i.e., asynchronous, refers to when the respective clock signals are different or undergo significant fluctuations during operation.